Graphitic high carbon-high vanadium steels



United States Patent 9 GRAPHITIC HIGH CARBON-HIGH VANADIUM STEELS Paul R. Borneman and Leonard V. Klaybor, Dunkirk,

N. Y., assignors to Allegheny Ludlum Steel Corporation, Brackenridge, Pin, a corporation of Pennsylvania No Drawing. Application November 9, 1955,

Serial No. 545,993

4 Claims. (Cl. 143-31) This invention relates to improvements in die steels tungsten and the balance substantially iron. These steels have exhibited superior resistance to abrasion, galling, scoring and scufling when used in such applications as cold working dies or liners for brick molds. These steels, however, have an inherent ditficulty in that high percentages of the carbide forming elements such as chromium, molybdenum, tungsten and particularly vanadium are required for the steel to obtain the requisite abrasion resistance. This has resulted in the steels possessing high percentages of the carbides of the respective elements with the result that each incremental increase in the carbides present in the structure of these steels has produced a corresponding decrease in the machinability of said steels.

An object of this invention is to provide a steel having a high resistance to abrasion and containing graphitic carbon, which steel possesses a controllable hardenability and excellent machinability characteristics.

A more specific object of this invention is to provide a steel containing carbon, silicon, manganese, chromium, tungsten, molybdenum, vanadium and the balance iron having a high percentage of carbides and suflicient graphite for the steel to possess excellent machinability.

These and other objects of this invention will become apparent when read in conjunction with the following de scription. i

In its broader aspects the steel of this invention comprises from about 1.5% to about 5.0% carbon, from about 1.4% to about 2.4% silicon, from about 1.10% to about 3.0% manganese, up to about 1% maximum chromium, up to about 1% maximum tungsten, up to about 1% maximum molybdenum, from about 3.0% to about 15.0% vanadium and the balance iron with incidental impurities.

The steel of this invention may be made and produced by any of the well-known steel mill practices, for example, electric arc furnace melting. Predetermined quantities of scrap and/or hot metal are placed in the furnace and melted to form a molten metal bath usually with a slag covering thereon. The details of the melting and refining of such steels are well known in the art and need not be described herein. After the molten metal is refined to obtain the steel of the desired chemical analysis, it is tapped into a ladle from which the molten metal is cast into ingots of predetermined shape and size. Upon solidification the ingots may be processed in any of the well-known manners, for example, by forging, pressing, extruding or hot rolling.

More specifically, the process used in the fabrication of "2.0% chromium, 0.25% to 2.0% molybdenum and/or the steel of this invention consists of heating the ingots 2,781,284 Patented Feb. 12, 195'? of the desired analysis to a temperature in the range between 1925 F. and 2025 F. at which temperature they are forged. After suflicient forging to break and distribute the as-cast structure, the steel may be hot rolled in any desired manner to form the semi-finished mill product, for example, billets, bars and the like. The hot rolled steel is annealed by heating to a temperature above the critical temperature and thereafter slowly cooled to a temperature below the critical temperature. In practice, it is preferred to anneal the steel at a temperature between 1400 F. and 1550 Fhand thereafter slowly cool the steel to about 500 F. The essential purpose of the annealing and the subsequent slow cooling is to promote the precipitation of graphite simultaneously with the spheroidization of thecarbides. This results in the steel being graphitized and thereby imparts the desired free machining properties thereto. The steel can be machined to any desired shape from which it is heat treated to obtain the desired physical properties of hardness, strength and ductility.

The preferred heat treatment to develop thephysical properties of the steel after graphitization consistsof a solution heat treatment at a temperature in the range between 1600 F. and 1750 F. for a time period of about 5 minutes to 4 hours depending upon the size of the piece being heat treated and followed by quenching in oil. This results in the steel having a hardness of about 60 Re to 65'Rc. The steel is then further heat treated by tempering at a temperature in the range between 300 F. and 1300 F. in order to increase the strength and ductility of said steel.

Reference may be had to Table I illustrating the chemical analysis of the general range, the preferred range, and steels A and AL-64 which are within the general range. It will be appreciated that in the following table where reference is made to iron comprising the balance of the steel, it is to be understoodthat the usual impurities found in such steels are also included, for example, not more than 1.5% of such elements as copper, cobalt, nickel, sulfur, phosphorus and the like.

TABLE I Percent by weight General range Preferred Steel A AL-flt range 1.54.0- 2.90-3.10 3. 18 2. 1.42.4. 1.60-1.90--. l. l. 89 0.10-3.0 1.01.2. 0.13 1.16 Up to 1.0 m 0.45 mar 0. 41 0. 04 Up to 1.0 max... 0.5 max.. 0.05 O. 09 Up to 1.0 max.-- 0.25045 0.30 0. 43 15.0-15.0. 7.75-8.25 8.02 8. 25 Bal. a1 Bal. Bal. U.0l-1.5 0 3-1 U.- 0. 57 0.91

Each of the elements given hereinbefore in Table I performs a specific function and therefore each element is required to be maintained within the range given. Carbon in the amount between 1.5% and 5.0% is needed to form the desired carbides for imparting high abrasion resistance as well as suificient excess carbon above the amount needed to form the carbides for the purpose of forming graphite for imparting the requisite machinability characteristics to-the steel. It is preferred to maintain silicon in the range between 1.4% and 2.4% because silicon is the predominant element in this steel for promoting graphitization upon proper heat treatment. Manganese in the general range given imparts sufiicient hot workability and provides the requisite deep hardenability. By controlling the amount of manganese present in the steel it is possible to control the amount of hardenability as will be described hereinafter. The complex carbide forming elements chromium, tungsten andmolybdenum,

within the ranges given, contribute to both the harden ability'an'cl rush-amass developed during heat treatment in addition to combining with a portion of the carbon to form carbides Whichcontr-ibute .to the-strength and-abrasion resistance of the steel. Careful control:of the amount-oftheserelements presentin the steel is .necessary since each has an inhibiting eiiect-onthe formation .of graphite and incremental increases -;in the .amount of these elements present in the analysis will cause corresponding-reductions in thetamountfloftgraphite which can :be precipitated 'during'annealing. Vanadium is the chief carbide forming element within ttheranalysis .of the I alloy ofthisinvention and :combines with :lar-geriportiomof the carbon .to form ca-rhides with ithe result that the steels show -:a high iresistanc'e to. abrasion, :galling scoring and scufiing.

As-a .spccificiexample .otthe steel of .thisjinvention,=steel 'A was made with the -a'nalysissas zgiven :hereinhefore in :Table I. :Steel :A' was iforge'cl :and ttherieafter ;hot rolled froma temperature of;l95.0 Rintoab'ar form ,frorn-awhich it wasiannealed at -.1450.F.iand-.slowly cooled therefrom. The 'annealingzh'eat treatment.an dsubsequentj slow cooling caused the formation of spheroidaltcarbides within the mi r tr tu ei with 057% .LIGHTbQD :hein-g;.present in the =form-of graphite. vThis:steehwas machined to theidesired shape which was then solutionrheattreated by Eheat'ing ;it at-atemperature of 1675 l ffor-Ltwothours followedby an oil quench. This hardeningrheat treatmentresultedin steelA havinga hardness ofbetween 63iRc and 64 Re. After tempering at a temperatureiof 400 for .-2hour's, *s'aid'ste'el showed an increase in strength and-ductility slifiicient for use, :for example-gas a cold working dieror as a linerforiibrick molds.

As was stated hereinbefore, manganese:-is essential-to provide the-requisite hardenability in the steel of this invention. This is more clearly illustrated lay-comparing the hardenability'data of steels A and -AL'64listedin 'T able I. These' steels have-substantiallysimilar composi tions withthe'bXcePtionbf manganese. f R'e'fer-ence rnay "be had toTable -II Whitman-rains the test results "obtained on 'a' standard lo'rnny Test for 'rne'a'suri'ng the depth of -penetra'tion-of the hardness -fors'teel-A- andsteel LAD-64.

TABLE'IL- H ARDENABILITY [Rockwell C hardness] Dlstanncle ifirom quenched'en'd "Steel A Steel AI2=64 of an inch As is evident fror'n'Tabl'eil, increasingflthe.mariganese fcontentto'a'ljout 1% increases the depth of penetration or hardness as ,measured .at the 50%. 'iriartensite point from h et /16 'for area A to su ar in steel AL''64. "Itis clearly evide'n "that ere deepeir'harderiability isl'dsired itasmangsnes content'shduldbe'abl'east Tl"% '"andpreierablylit should be fniaintainedjne'ar the higher end of the preferred range 'gived'he'reinbefore i'n'Tabll.

I 'thefdesired characteristics.

The steel of this invention has excellent machinability which can be demonstrated relatively by sawing with a power hacksaw. The power hacksaw test consists of cutting two-inch square billets under identical conditions. In this test the billets are sawed on a power hacksaw using a new molybdenum type high speed steel blade. After the initial cut is made, the material is advanced and a second cut is made. The speed or downward feed of the power hacltsaw is increased in each succeeding cut to increase the severity-of the test until the point is reached where the blade shows excessive wear or breaks, whichever occurs first. The number of cuts and the relative speeds of the saw incacn cut compared to the number of cuts and the relative speed for the hacksaw blade in the standard or comparative steel-gives-a measure of the relative machinability of the steels.

In applying the above described test to determine the relative .machinahility of the steel .of this invention as compared to another steel having .the same degree of resistance to abrasion, galling, scoring and scufling in .the hardened state, a steel having the following analysis 'was-usedasnhe standard: about 291% carbon, about 0.37% Lmanganese,. about 0.35% silicon, about 0.11% tungsten, about :0.90 chromium, about 0.96% molybdenum,.about 10.45vanadium and the balanceiron with incidental impurities. The standard steel was hot worked .intoa two-inch square billet which was annealed to a har'dnessof .about 1269 BHN. Metallographic and wet .chemical analysis .failed .to .showthe presence of graphite -i-n thejstan'dard steel in the annealed condition. Steel "AL-#64 haVingtheJanalysis givenhereinbefore and in the forrn of a ,twoainch .square t billet was then compared .to =the=standards teel, it being noted :-that steel AL 64 had :about 0;9l graphite after annealing'at 1450 Rand-a hardness of =2695BHN.

Steel A L=64-was subjected to five successive cuts across the section of the two-inch-billetusingianew molybdenum "t y-pe -h-igh=sp'eed'- steel bladezhaving :6.-teeth per inchwith the speed of the blade being increased with each successive cut. After t-he 'fifth-cut, the-blade showed some wearand --t-he cutting-was stopped on steel AL-64. .After-an. identi- -cally new' hacksaw blade was inserted inthe power hacksaw, the standardsteel'of the analysis givenhereinbefore *was-sawed in thesame manner as steel AL-64. The speed "of the hacksaw was adju'stedso that substantially the same *speed 'was used-for-each cut-0n the standard steel-as was usedon the-same-numbered cut-on-steel -AL'64. .It was found-that after the first cut through thestandardsteel,

"'the bl'ade showed" some wear, and before'the second cut could-becompleted,thesaw'blade broke. ilt is significant to point out that the speed of the saw blade was more "than twice as fast during thefifthcut onsteel AL64 as compared-to thespeed of the-'sawblade during-the second cut on the --standard steelwhich broke :the blade. It is evident from the above-describedtest-that the steel of'this invention possesses-a superior machinability to that of comparable steels having substantially the same resistance to abrasion, galling, scoring and-scuiiing. It is believed thatthe superior machinability has been achieved by the graphite which is-present through acritical proportioning ofj'the' alloying elements cooperatingwiththe heat treatment given hereinbefore to promote-graphitization, thereby imparting the requisite machinabilityproperties'thereto.

There'L-are' nospecial techniques, processing-or equipment 'used in the production of this steel in orderto obtain 0 In addition, 1 there is a noticeable'absence of 'strate'gicand costly alloying-elements, thus .makingthe steel =valuable iroin-the economical aspect.

Weclaim: 1. An iron alloy' possessing excellent macliinability characteristics, superior resistance to abrasion, scoring, sending and galling and controllable -hardenabii-ity and consisting of, fromabout 1.5%to 'about;5.0%- carbon, from'about 1.4%;toabo-ut 2.4% :silicon,-fr om about- 0.10%

to'about 3.0% manganese, up to 1.0% 'chromium,-upto l l l 1 1.0% tungsten, up to 1.0% molybdenum, from about 3.0% to about 15.0% vanadium and the balance iron with incidental impurities, the alloy having from about 0.01% to 1.5% of carbon present in the form of graphite resulting from heat treatment at a temperature in the range between 1400 F. and 1550 E, and slowly cool ing therefrom.

2. An iron alloy possessing excellent machinability characteristics and superior resistance to abrasion, scoring, scufling and galling and consisting of from 2.90% to 3.1% carbon, from 1.60% to 1.90% silicon, from 1.0% to 1.2% manganese, up to 0.45% maximum chromium, up to 0.5% maximum tungsten, from 0.25% to 0.45% molybdenum, from 7.75% to 8.25% vanadium, and the balance iron with incidental impurities, the alloy having from about 0.3% to 1.0% of carbon present in the alloy in the form of graphite resulting from heat treatment at a temperature in the range between 1400 F. and 1550 F., and slowly cooling therefrom.

3. An iron alloy for use as a cold Working die and containing about 3.18% carbon, about 1.95% silicon, about 0.13% manganese, about 0.41% chromium, about 0.05% tungsten, about 0.3% molybdenum, about 8.02% vanadium, and the balance substantially iron with incidental impurities, the alloy having about 0.57% of carbon present in the alloy in the form of graphite resulting from treatment at 1450 F. and slowly cooling therefrom.

4. An iron alloy for use as a cold Working die and having a deep hardenability and containing about 2.90% carbon, about 1.89% silicon, about 1.16% manganese, about 0.04% chromium, about 0.09% tungsten, about 0.43% molybdenum, about 8.25% vanadium and the balance substantially iron With incidental impurities, the alloy having about 0.91% of carbon present in the alloy in the form of graphite resulting from heat treatment at 1450 F., and slowly cooling therefrom.

No references cited. 

1. AN IRON ALLOY POSSESSING EXCELENT MACHINABILITY CHARACTERISTICS, SUPERIOR RESISTANCE TO ABRASION, SCORING, SCUFFING AND GALLING AND CONTROLLABLE HARDENABILITY AND CONSISTING OF, FROM ABOUT 1.5% TO ABOUT 5.0% CARBON, FROM ABOUT 1.4% TO ABOUT 2.4% SILICON, FROM ABOUT 0.01% TO ABOUT 3.0% MANGANESE, UP TO 1.0% CHROMIUM, UP TO 1.0% TUNGSTEN, UP TO 1.0% MOLYBDENUM, FROM ABOUT 3.0% TO ABOUT 15.0% VANADIUM AND THE BALANCE IRON WITH INCIDENTAL IMPURITIES, THE ALLOY HAVING FROM ABOUT 0.01% TO 1.5% OF CARBON PRESENT IN THE FORM OF GRAPHITE RESULTING FROM HEAT TREATMENT AT A TEMPERATURE IN THE RANGE BETWEEN 1400* F. AND 1550* F., AND SLOWLY COOLING THEREFROM. 